Electrical machinery, such as direct current motors for example, uses brushes for transferring power between an electric circuit and a commutator. The brushes are in contact with the rotating commutator and during use wear and erode from such contact thereby causing them to shorten in length. The brushes must be replaced when sufficiently worn to prevent damage to the commutator and insure efficient power transfer. Some current devices signal when the brushes are sufficiently worn to need replacing but usually interfere with the movement or usability of the brush. It is desirable to have a device which signals when the brushes have been worn away to a length at which replacement of the brush is desirable and does not interfere with the movement of the brush.